Probably derived from the old Celtic name Rigantona meaning "great queen". It is speculated that this was the name of an otherwise unattested Celtic goddess of fertility and the moon. The name Rhiannon appears later in Welsh legend in the Mabinogion, borne by the wife of Pwyll and the mother of Pryderi.
Hefeydd. ... Heyfedd Hir (Hir meaning "long" in Welsh, but also referring to distance in time), is mentioned as one of the Seven Knights left to take charge of the Island of Britain when Bran went to rescue his sister in the second branch of the Mabinogion.
